The goal of the proposed research will be to understand the role that a novel integrin plays in the biology of the mast cell. Mature mast cells localize to different tissues to accomplish different functions within the antigen specific, IgE, arm of the immune response. The mechanism by which a mast cell knows where its eventual destination is has not been explored although the past consensus has been that these cells localize in response to specific cytokine/lymphokine requirements not a homing receptor. We have found that mature mucosal mast cells express a novel beta integrin and we hypothesize that this integrin, in association with one or more alpha chains, localizes mast cells to specific tissues. The proof of the hypothesis is the research proposed in this application. First, the cell surface expression of this beta integrin must be confirmed and the alpha chains it is associated with be identified. The modulation of expression of these integrin chains will be studied under varying conditions of mast cell differentiation. Cell surface expression of these chains will be monitored via the use of pre-existing antibodies those we derive specific for these integrin molecules. The identification and isolation of novel beta and/or alpha integrin chains will be accomplished via the cloning of such genes either through PCR amplification of conserved coding sequences, low stringency hybridization with other integrin chain cDNA's, or peptide sequencing of novel integrin chains identified as partners to known integrin chains. The homing function of these complexes will be confirmed via blocking antibody, antisense constructs, or functional transfer of homing activity via transfection of the beta and alpha chain coding sequences into a cell that does not normally express them. Homing anayses will be done both in vitro and in vivo using normal and mast cell deficient strains of mice. The final proof of this homing function will be in the generation of mice lacking the beta and/or alpha chain expression through homologous recombination with a defective gene sequence. Using this mix of genetic, cell biology and biochemical experimental approaches, the roles of these integrin complexes in the biology of the mast cell will be determined.